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private JButton createButton(String text, ActionListener action){
 JButton button = new JButton(text);
 button.addActionListener(action);
 button.setFocusable(false);
 return button;
}
private JButton createMemoryEraseButton(){
 return createButton("ME",(e)->memoryStore.resetStoredValue());
}
private JButton createMemoryRecallButton(){
 return createButton("MR",(e)->{
 display = screen.getText();
 screen.setText(display + "" + memoryStore.getStoredValue());
 });
}
// ....
private void createOperationButtons() {
 operationButtons = new JButton[] {
 createMemoryEraseButton(),
 createMemoryRecallButton(),
 // ....
 };
}

private JButton createButton(String text, ActionListener action){
 JButton button = new JButton(text);
 button.addActionListener(action);
 button.setFocusable(false);
 return button;
}
private JButton createMemoryEraseButton(){
 return createButton("ME",(e)->memoryStore.resetStoredValue());
}
private JButton createMemoryRecallButton(){
 return createButton("MR",(e)->{
 display = screen.getText();
 screen.setText(display + "" + memoryStore.getStoredValue());
 });
}
// ....
private JButton[] createOperationButtons() {
 operationButtons = new JButton[] {
 createMemoryEraseButton(),
 createMemoryRecallButton(),
 // ....
 };
 return operationButtons;
}

You could even go one step further and move the method createOperationButtons() and all the create??Button() methods in to a separate class.

Off cause, all the objects these methods work on you would have to pass in as prarameters either to the constructor of the new class or the createOperationButtons() method and subsequently to the create??Button() methods as needed.

I have to do it 18 times in one method it makes the method very big and ugly. There has to be a way of making it nice and clean. – Alex. M

You cannot avoid having to specify the different behavior for the operator buttons.

In your first solution the ugliness was the if/else cascade in your actionPerformed() method.

With my suggestion you could at least ease the readers pain by having an additional method for each operator button:

private JButton createButton(String text, ActionListener action){
 JButton button = new JButton(text);
 button.addActionListener(action);
 button.setFocusable(false);
 return button;
}
private JButton createMemoryEraseButton(){
 return createButton("ME",(e)->memoryStore.resetStoredValue());
}
private JButton createMemoryRecallButton(){
 return createButton("MR",(e)->{
 display = screen.getText();
 screen.setText(display + "" + memoryStore.getStoredValue());
 });
}
// ....
private void createOperationButtons() {
 operationButtons = new JButton[] {
 createMemoryEraseButton(),
 createMemoryRecallButton(),
 // ....
 };
}